Add token-only.

[jefferai]

Fixes #2855

[chrishoffman]

This looks good to me. My only question is should -token-only also imply -no-store? I know the flag could be set to disable storage but it seems to me the use case for -token-only would rarely, if ever, need the token to be stored.

[jefferai]

@chrishoffman I had thought about that too, and wasn't sure. I guess it depends which problem is being solved:

• The token is returned and stored in the token helper but the user doesn't understand where that is, so when they want to pass it into a script they don't know where to look
• The token is never meant to be used locally and always passed on

I guess the former situation can be remedied by them simply passing the value back into vault auth if needed. So probably it should imply no-store. I'll make that change.

[briankassouf]

👍

[martinssipenko]

Nice, thanks!